U.S. · Shipping
USPS tracking number checker.
Paste a tracking number to see how it breaks into parts and whether its last digit matches the USPS check-digit rule.
Tracking number
Result
Most USPS tracking numbers you meet are 22 digits, and the last digit is not random. It is a check digit that lets any system notice a mistyped or misread number before it asks USPS about a package that does not exist. This page applies that arithmetic in your browser and splits the number into the fields USPS Publication 199 defines. It does not look up any package.
How this is calculated
Publication 199 builds the package identification code from a two-digit channel application identifier (92, 93 or 94 in the current layouts), a three-digit service type code, a six- or nine-digit Mailer ID (a nine-digit one starts with 9), a serial number and a final mod 10 check digit. Commercial layouts with a nine-digit Mailer ID come to 22 digits, and the longer serial options reach 26. When the barcode also carries the routing prefix, the data string is 30 or 34 digits: the three-digit 420, a five- or nine-digit ZIP Code, then the 22-digit code. This page strips that prefix before checking.
The check digit follows section 4.6. Starting with the digit next to the check digit, weight the digits 3, 1, 3, 1 and so on from the right, add the results, and the check digit is the amount that brings the total up to the next multiple of 10. The 13-character S10 format (two letters, eight digits, a check digit, a two-letter country code) uses a different rule from the Universal Postal Union: multiply the eight serial digits by 8 6 4 2 3 5 9 7, divide the sum by 11, subtract the remainder from 11, and use 0 for a result of 10 and 5 for a result of 11. Data retrieved 2026-10-26 from the two documents linked below. Layouts change, and Pub. 199 is the version dated 1/19/2024.
Worked example
A 22-digit code. Publication 199 itself uses 9212 3912 3456 7812 3456 7 plus a check digit. The digits in the even positions counted from the right add to 45 and are multiplied by 3, giving 135. The digits in the odd positions add to 45. The total is 180, already a multiple of 10, so the check digit is 0 and the full code is 9212391234567812345670. Change the last digit to 1 and the page reports a mismatch and the expected 0.
An S10 code. The UPU standard works through the serial number 47312482. The weighted values 32, 42, 12, 2, 6, 20, 72 and 14 add to 200. 200 divided by 11 leaves a remainder of 2, and 11 minus 2 is 9, so the self-checking number is 473124829. Add a service indicator and country code, for example EA473124829US (the letters here are placeholders), and the page confirms the structure.
Mistakes people make
- Treating a good check digit as proof of a parcel. It shows the number is well formed. Only USPS Tracking shows whether a package exists and where it is.
- Typing the number without its first two digits. The channel identifier is part of the number.
- Pasting the barcode data string. A 30 or 34 digit string includes the 420 and ZIP Code. This page removes them, but the tracking number you give a customer should not include them.
- Using this for other carriers. UPS, FedEx and Amazon numbers follow different formats.
Who this is for, and what it does not cover
It suits sellers, shipping clerks and anyone reconciling a spreadsheet of tracking numbers who wants to catch typos in bulk before querying USPS. It does not check service type codes against USPS's current table, does not decode older formats beyond the length and check-digit test, and does not cover the Intelligent Mail barcode used on letters and flats, which is a different code.
FAQ
Does a USPS tracking number have a check digit?
The long IMpb numbers do. The last digit is a mod 10 check digit calculated from the digits before it, using the method in USPS Publication 199 section 4.6. The 13-character S10 codes also carry a check digit, calculated by a different rule.
Why is my number 22 digits?
Publication 199 builds it from a two-digit channel identifier, a three-digit service type code, a Mailer ID, a serial number and the check digit. The common commercial layout with a nine-digit Mailer ID and seven-digit serial adds up to 22 digits.
What does it mean if the check digit fails?
The number has probably been mistyped, truncated or misread. Compare it against the original label or receipt. A passing check digit does not guarantee the number is in use.
What are the 92, 93 and 94 at the start?
Publication 199 calls them channel application identifiers. They show how the barcode was generated: 92 for commercial layouts with a nine-digit Mailer ID, 93 for those with a six-digit Mailer ID, and 94 for online mailers.
What is an S10 tracking number?
A 13-character identifier of two letters, eight digits, a check digit and a two-letter country code, defined by the Universal Postal Union. Publication 199 notes that an S10-type barcode is allowed for international shipments.
Can this tell me where my package is?
No. It runs in your browser and contacts nothing. Use USPS Tracking with the full number for status.
Common mix-ups
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Often assumedThe first two digits, such as 92 or 94, are only a routing prefix and can be dropped when you type the number.
What the source saysPub. 199 says the channel application identifier is part of the tracking number and that the full number, including it, must be given to the customer so they can track the package. [1]
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Often assumedThe 420 and the ZIP Code printed in the barcode are part of the tracking number.
What the source saysPub. 199 says the 420 identifier and the ZIP Code are suppressed in the human-readable text, and the check digit is calculated on the package identification code without them. [1]
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Often assumedInternational-style 13-character codes use the same check digit as the long domestic numbers.
What the source saysThey do not. The long domestic code uses a mod 10 check (weights 3 and 1), while the 13-character S10 code uses weighted modulus 11 with weights 8 6 4 2 3 5 9 7 over its eight serial digits. [2]
Checked against these sources on .
Sources
Retrieved 2026-10-26. Each source was opened and read against the claim next to it.
- USPS Publication 199, Intelligent Mail Package Barcode (IMpb) Implementation Guide, version 29 (1/19/2024): sections 4.1 to 4.6: channel application identifiers 92, 93 and 94, the three-digit service type code, six- and nine-digit Mailer IDs, the final mod 10 check digit and its worked calculation, and the note that the 420 routing prefix and ZIP Code are excluded from the check.
- UPU standard S10-12, identification of postal items, 13-character identifier (approved 17 October 2017): section 5: the 13-character layout and the weighted modulus 11 check digit with its 47312482 worked example.
- USPS Tracking: where package status comes from; a check digit cannot tell you this.
General information only
This page is general information, not legal, compliance or financial advice. Rules, formats and registries change, and your facts may differ. Confirm anything that matters with the issuing agency or a qualified professional. Everything runs in your browser; nothing you enter is sent anywhere.